1. Field of the Invention
The invention pertains to a vibration damper with amplitude-selective damping force having a piston arranged in a cylinder and dividing the cylinder into two working spaces, the piston including a flow connection controlled by an axially movable switching ring in response to the movement of the piston rod.
2. Description of the Related Art
A vibration damper with amplitude-selective damping force is known from U.S. Pat. No. 5,823,306. This damper has a piston arrangement comprising a lower and an upper valve, which are kept a certain distance apart by a spacer. The two valves are each equipped on both sides with damping valve disks and at least one check valve disk. A switching ring with freedom of axial movement is installed between the two valves. Depending on the direction in which the piston rod is moving, the switching ring comes to rest against one or the other of the facing valve disks of the two valves and thus releases or blocks an annular gap between the valve disks and the inside wall of the cylinder.
U.S. Pat. No. 6,352,145 also describes a vibration damper with amplitude-selective damping force with a piston arrangement having an axially movable switching ring which controls a flow connection through a hollow piston rod pin. An outlet of the flow connection is provided upstream of a stop surface for the switching ring. As a result, noise problems can be partially solved. It is necessary, however, to tolerate the fact that a change in the amplitude-selective damping force is possible only in the outward-travel direction of the piston rod and that the piston rod must travel a certain “dead” distance, namely, the distance between the outlet opening and the stop surface, before an amplitude-selective change in the damping force can go into effect in the outward-travel direction.